[Issue 16395] New: auto return on override

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=16395

          Issue ID: 16395
           Summary: auto return on override
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Keywords: spec
          Severity: enhancement
          Priority: P1
         Component: dmd
          Assignee: nobody at puremagic.com
          Reporter: lodovico at giaretart.net

Currently DMD does not allow returning auto when overriding a function.

Consider this case:

===========================================
interface Foo { /* some methods */ }
interface Bar { Foo getFoo(); }

class BarImpl: Bar
{
    override auto getFoo()
    {
        class FooImpl: Foo
        {
             // implementation of Foo ...
             // ... plus range methods
        }
    }
}
===========================================

Currently I have two options:
1) remove auto and return Foo instead; this way the user cannot use the range
interface of FooImpl, because it receives a Foo
2) put FooImpl outside the function and return FooImpl; this way all
functionality is correct, but it's not optimal as I have to put FooImpl outside
the only function that uses it (which looks weird), plus FooImpl cannot
implicitly access the getFoo context.

This is not a essential enhancement, I don't know if it is feasible to
implement it, but it would make the language features more orthogonal, allowing
the use of overriding with return type inference and voldemort types.

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